1. Field of the Invention
The present invention relates to liquid crystal display (LCD) devices, and more particularly to an LCD device including a diffuser.
2. Discussion of the Related Art
Owing to their small size, light weight, and low power consumption, flat panel display (FPD) devices have been the subject of much research in the field of information technology. Among the many types of FPD devices, LCD devices have excellent color, resolution, and display characteristics and are used in devices such as notebook personal computers (PCs), desktop PCs, etc. Generally, LCD devices include first and second electrode bearing substrates coupled to, and spaced apart from each other by a layer of liquid crystal material. LCD devices exploit anisotropic optical properties of the liquid crystal material and display images. In particular, electric fields generated when a voltage is applied to the electrodes on the substrates can selectively manipulate the light transmittance characteristics of the liquid crystal material.
FIG. 1 illustrates a cross-sectional view of a liquid crystal cell in a related art transmissive-type LCD device.
Referring to FIG. 1, liquid crystal cells generally include first and second transparent substrates 10 and 20, respectively, that are coupled to, and spaced apart from each other by a layer of liquid crystal material 30. A thin film transistor (TFT) “T” is arranged on an inner surface of the first substrate 10 and includes a gate electrode 11, a gate insulating layer 12, an active layer 13, an ohmic contact layer 14, a source electrode 15a, and a drain electrode 15b. A passivation layer 16 covers the TFT and includes a contact hole 16c exposing the drain electrode 15b. A pixel electrode 17 made of transparent conductive material is formed on the passivation layer 16 and contacts the drain electrode 15b through the contact hole 16c. 
A black matrix 21 is arranged on an inner surface of the second substrate 20 at a position corresponding to the location of the TFT on the first substrate 10. Individual color filters 22a and 22b are provided on the black matrix 21 and include one of red (R), green (G), and blue (B) filters. Each color filter is arranged in a location corresponding with the location of a respective pixel electrode 17 on the first substrate 10. A common electrode 23 made of transparent conductive material is formed on the color filters 22a and 22b. 
A layer of liquid crystal material 30 is provided between the pixel and common electrodes 17 and 23, respectively. When a voltage is applied to the pixel and common electrodes 17 and 23, respectively, molecules within the liquid crystal material 30 become realigned and the light transmittance characteristics of the light crystal material 30 may be altered. Although not shown, orientation films are formed on the pixel and common electrodes to align the liquid crystal molecules within the liquid crystal cell.
Liquid crystal cells, by themselves, do not emit light. Therefore, images created by transmissive-type LCD devices are typically displayed using external light sources (e.g., backlights arranged under the first polarizer 41). The light generated by the external light sources is selectively transmitted by the liquid crystal cell.
First and second polarizers 41 and 42, respectively, are arranged on exterior surfaces of the first and second substrates 10 and 20, respectively, such that their respective transmission axes are oriented perpendicular to each other. The polarizers convert unpolarized light emitted by the external light source into linearly polarized light. Due to the presence of the first and second polarizers, only light having a polarization direction parallel to a transmission axis of each polarizer may be transmitted through the liquid crystal cell.
Provided with a backlight and the polarizers, transmissive LCD devices display images at a high brightness along a primary viewing angle while images are displayed at a low brightness along viewing angles outside the primary viewing angle. To compensate between the differences in brightness along the various viewing angles, diffusers are typically disposed over the liquid crystal cell to scatter transmitted light. Accordingly, diffusers allow LCD devices to display images at a uniform brightness over many viewing angles. In particular, diffusers capable of scattering light by holographic methods provide LCD devices with excellent viewing capabilities.
FIG. 2 illustrates a cross-sectional view of a related LCD device using a holographic diffuser.
Referring to FIG. 2, a first polarizer 50 may be arranged under a liquid crystal cell 40, wherein the liquid crystal cell 40 includes a layer of liquid crystal material 45 provided between two substrates 41 and 42 having electrodes 43 and 44. A backlight 60 is arranged under the first polarizer 50 while a holographic diffuser 70 and a second polarizer 80 are sequentially arranged over the liquid crystal cell 40.
Typical holographic diffusers 70 include an upper diffusing layer 71 and lower overcoat layer 72, both made of organic material. The topography of a lower surface of the diffusing layer 71 includes a holographic pattern. The overcoat layer 72 includes an upper surface that conformally contacts the lower surface of the diffusing layer 71 while a lower surface of the overcoat layer 72 presents a substantially planar surface to the liquid crystal panel 40. The diffusing layer 71 and the overcoat layer 72 have different refractive indices and scatter light transmitted to the second polarizer 80.
As the difference in the refractive index between the diffusing layer 71 and the overcoat layer 72 increases, the diffusion angle of the holographic diffuser and the viewing angle of the LCD device increases. Generally, differences in refractive index of over about 0.3 are achieved by providing the diffusing layer 71 with a refractive index greater than about 1.6 and the overcoat layer 72 with a refractive index less than about 1.3.
Use of the aforementioned holographic diffuser is disadvantageous, however, in that organic materials with low refractive indices have poor adhesive characteristics and forming overcoat layers conformally over the holographic pattern diffusing layers is a complex, time consuming process. Accordingly, LCD devices fabricated with the aforementioned holographic diffuser tend to be expensive and have a low reliability.